1. Field of the Invention
The invention relates to a surface mount type antenna. More particularly, the invention relates to a surface mount type antenna comprising a dielectric/magnetic base having first and second main surfaces opposite from each other and side surfaces substantially perpendicular to the main surfaces, a feed electrode disposed on the base, a ground electrode disposed on the base, and a radiation electrode disposed on the base and having an open-circuited end capacitively coupled to the feed electrode and a short-circuited end connected to the ground electrode. The surface mount type antenna is used for mobile communication apparatus and a communication apparatus using the antenna.
2. Related Art
FIG. 7 shows a prior art antenna apparatus. A member 11 shown in the figure is a dielectric base. Electrodes 22b, 23b, 21a, 21b and 21c are formed on side surfaces of the dielectric base 11. Electrodes 22a and 23a are formed on the lower main surface as viewed in the figure. In these electrodes, the electrodes 22a, 22b function as a feed electrode, the electrodes 23a, 23b function as a ground electrode, and the electrodes 21a, 21b, 21c function as a radiation electrode. An electrostatic capacitance is thereby formed between an open-circuited end of the radiation electrode (an end portion of the electrode 21c) and the feed electrode 22a, 22b. The radiation electrode is excited by the capacitive coupling through this electrostatic capacitance. Thus, the surface mount type antenna functions as a resonating type antenna.
The conventional surface mount type antenna shown in FIG. 7, however, has the problems that it entails an increased number of electrode forming steps because of the need to form electrodes over many side surfaces of the dielectric base.
The radiation electrode formation surfaces of the conventional surface mount type antenna shown in FIG. 7 may be modified to solve this problem. For example, as shown in FIG. 8, the radiation electrode indicated by 21a, 21b, and 21c are formed on the upper main surface and the right rear end surfaces of the dielectric base 11 as viewed in the figure. In this structure, the electrostatic capacitance produced at the gap between the open-circuited end of the radiation electrode (an end portion of the electrode 21c) and the ground electrode 23b can be increased and a predetermined resonant frequency can be set even if the inductance of the radiation electrode is small. Advantageously, therefore, the overall size can easily be reduced. However, since the end of the ground electrode 23b is positioned between the feed electrode 22a, 22b and the open-circuited end of the radiation electrode, the coupling between the feed electrode and the radiation electrode is reduced, resulting in a reduction in the ease of impedance matching to an external circuit.